Summary of WorkMass spectrometry is playing a significant role in the identification of unknown proteins at trace levels, in the identification of posttranslational modifications of proteins, and in the identification of proteins that are part of functional/disease related biological complexes. This information can be vital to understanding signal transduction pathways and the regulation of function of the involved proteins. Critical parts of this project are to develop procedures for handling and isolation of sub-picomole levels of proteins, specifically modified proteins (e.g., phosphorylated), intact protein complexes, and their digests in a manner compatible with the final instrumental determinations. Specific aims:1.Correlate surface accessibility with molecular modeling to provide tertiary structure prediction.2.Determine sites of interaction between proteins and DNA based on cross-linking an MS/MS identification of cross-linking sites and on protection assays.3.Characterize the regulatory domain of PP5 and its site of interaction.4.Elucidation of phosphorylation sites on p53 and of the interrelationship between phosphorylation of specific sites and biological activity. Biological processes often involve specific non-covalent and/or covalent interactions. Understanding the structures of functional intermediates and products is important in determining biochemical mechanisms and how specific molecules interact with endogenous compounds. Specific aims:1.Identify the amino acids of b-polymerase that can form the covalent intermediate with the abasic site in excision-repair.2.Identify amino acids phosphorylated on histones that are modulated in cells in response to treatment with dexamethasone.3. Determine sites and levels of phosphorylation and other posttranslational modifications on ?normal' p53 and on p53 phosphorylated in response to specific treatments, such as with environmental stresses and/or by phosphatase inhibitors, and correlate these changes with changes in biological function.